Process for protecting iron surfaces from corrosion.



SHERARD OSIBOBN COWPER-COLES, OF WESTMINSTER, LONDON, ENGLAND.

PROCESS FOR PROTECTING IRON SURFACES FROM CORROSION.

1,072,091. No Drawing.

Specification of Letters Patent.

A Application filed November 23, 1912. Serial No. 733,097.

To all whom it may concern Be it known that I, SHERARD Osnonnv followsthat is to say, I first remove all scale, grease and oxid from thearticles to be treated, in any of the well known manners, such as bypickling or sand blasting, and I then electro-deposit upon them acoating of iron as pure as possible. The iron may be deposited from anysuitable electrolyte, for example, ferrous sulfate. The articles afterhaving been coated with pure or practically pure iron, are washed andthen placed in a second vat, in which a coating of zinc or zinc-ironalloy is deposited upon the pure iron.

I would here remark that a thin coating or film of chemically pure ironhas been suggested by other workers as a basis for the deposition ofmetals such as tin, nickel and copper, but whereas they deposited a filmof iron, with the object of increasing the adhesion of the metalsubsequently to be deposited upon the iron, I cause a comparatlvelythick coating of pure iron to be deposited upon the iron or steel, whichdeposit, being slightly electro-positive to the underlying metal, actsin itself as a protective coating. In fact, in many cases, the amount ofiron deposited exceeds the amount of zinc or zinc-iron alloysubsequently deposited thereon.

In a modification of the invention, I may advantageously effect thedeposition of both iron and zinc or zinc-iron alloy from the sameelectrolytic bath, which is made up of a mixture of zinc and iron salts.When this procedure is adopted, a low current density is employed in thefirst instance, so

as to deposit iron, and toward the end of the depositing process, thecurrent density is increased, in order to deposit a zinc-iron alloy. Theelectrolyte is made up with iron and zinc sulfates, about 20 ounces ofthe crystallized salts of each metal to each gallon of water. Insolubleanodes are employed in conjunction with small iron anodes, and theelectrolyte circulated over scrap zinc, in order to keep the zinccontent in the electrolyte the same. The relative proportions of zincand iron in solution are varied according to the current density it isdesired to employ, which varies with the class of work to be coated,whether flat work or work having deep hollows. The current densityusuallyemployed ranges from 5 amperes to 20 amperes or more per squarefoot of cathode surface.

In some cases the articles may finally be subjected to a heating orbaking process, to effect a closer union of the deposits with thesurface of the articles.

Claims:

1. A process for protecting iron and steel surfaces from corrosion,which consists in first depositing a thick protective coating ofsubstantially pure iron upon the prepared surface and then depositingupon the protective coating, a further protective metallic coating.containing zinc.

2. A process for protecting iron and steel surfaces from corrosion,which consists in first depositing a thick protective coating ofsubstantially pure iron upon the prepared surface, then depositing uponthe iron a coating of zinc alloy and then subjecting the same to a finalheating or baking treatment.'

3. A process for the protection of iron and steel surfaces fromcorrosion, which consists in subjecting the same to an electrolytic bathcomposed of zinc and iron salts, employing a low current density toeffect the deposition thereon of iron, and then increasing the currentdensity to effect a deposit of zinc iron alloy.

SHERARD OSBORN GOWPER-GOLES.

Witnesses WM. BRADDOCK, G. L. BUTLER.

Patented Sept. 2, 1913.

